Spears, 21, announced her news on Twitter, and posted a picture of she and her fiance, as well as a gorgeous closeup of her ring. “Guesssss what??????” she wrote next to the picture.

Minutes later, she posted another photo: a close-up of the huge, round-cut diamond. “He did good,” she wrote, with a smiley-faced emoticon.

This will be the first marriage for the former Nickelodeon star. She was previously engaged to Casey Aldridge, the father of her 4-year-old daughter, Maddie. They split for good in 2010.

Spears’ engagement comes just two months after news of her older sister’s broken engagement. Britney, 31 — married twice before, to pal Jason Alexander and ex Kevin Federline, with whom she has two kids — was set to wed boyfriend Jason Trawick until the couple’s January 2013 split.

That is one of the more beautiful engagement rings I’ve seen in a while! It’s simple, yet beautiful!

Makes me nervous that she’s getting married so young…. but hopefully it works out. I was married at 22 – and while I’m still married now, I will say getting married that young is harder! Pretty hard to not be selfish when you’re 21 years old.